Learn me making templates

So, im at the point of mating the body to the chassis and final trimming wheelwells. Kinda nervous if im honest. 

Im going to need to make a bunch of pieces to close gaps to the passengers compartment and none of them are going to be the same. Nor will they be easy to access. 

The following picture is of the firewall to cowl panel. Now, the firewall is flat-ish, and the cowl is curved. Additionally the cowl is misshapen due to damage. Id like to fix that as well. I know i can take a raduis template off the cowl of an undamaged car, but haven't figured out how to do that. Then, i can make a negative for the underside to make the firewall to cowl filler at the same time getting the damaged cowl back into shape.  How do i do this? What materials and processes? 

Then, closely behind cones the wheelwells. I have butchered the rears already to the point im going to have to fix some of my work. This is due to not having a good cut line.  I tried tracing the tire with a sharpie and cutting. Obviously in hindsight that was an error. How do i make a template of the needed wheelwell opening from a loose tire and line it up on the axle centerline far enough out that i can trace and cut it? 

When I cut the wheelwells on my buddy's "Miata", I hung the fender, then put a wheel/tire against it, lined up with the wheel on the car.  Simply traced the outer tire with Sharpie, and cut the fiberglass with a Dremel rotary disc.  Had to do some final touch-up to the shape, but worked quite well.  YMMV with steel.

For templates, we use CAD --- Cardboard Assisted Design.

For panel gaps, poster board and tape. Build up the larger shape from smaller pieces.

For the rear wheels, make a radius gage from wood/sharpie and attach the center to the wheel at the desired heights.

stafford1500 said:

For panel gaps, poster board and tape. Build up the larger shape from smaller pieces.

For the rear wheels, make a radius gage from wood/sharpie and attach the center to the wheel at the desired heights.

Care to example a radius gauge? 

Also, how to i transfer the large gradual radius curve to cardboard? Im just not seeing the process in my head the way i have with straight pieces and bends.

I have used a sharpie on a string to give me a nice circle for a wheel opening.